The sister of murdered student Meredith Kercher has spoken of the "fear and terror" she must have felt on the night she died.

Stephanie Kercher made the comments in a documentary about Amanda Knox, who was reconvicted of murdering the 21-year-old in the Italian town of Perugia in 2007 last month following a second trial.

Only one person - Rudy Hermann Guede - is currently behind bars for her murder after American Knox and her former boyfriend, Italian Raffaele Sollecito, successfully appealed against their original guilty verdicts. Afterwards Knox returned home to America and has so far refused to go back to Italy to serve her jail term following her second conviction, saying she will only be extradited "kicking and screaming".

The BBC Three documentary Is Amanda Knox Guilty? also hears from lawyers and experts from both the defence and the prosecution teams and contains the audio of Knox's prison interrogation after her arrest when she was asked why she told police that her manager from the local bar where she worked had committed the crime.

Ms Kercher told the programme she feels her sister "has been forgotten" in the media storm surrounding Knox.

"Mez has been forgotten in all of this," she said. "The media photos aren't really of her. There's not a lot about what actually happened in the beginning. So it is very difficult to keep her memory alive in all of this."

She said her sister did not deserve what happened to her: "Everything that Meredith must have felt that night. Everything she went through. The fear and the terror and not knowing why. She didn't deserve that. No one deserves that," she said.

"We all definitely want some sort of closure. Just having an end of the Italian justice system and knowing that's the final decision, and then we can start to remember just Meredith."

Speaking of when she last saw Meredith alive as she prepared to study in Italy as part of her Leeds University course, Ms Kercher said: "She was very excited about coming to Italy, looking forward to learning about Italian culture. Seeing the city of Perugia and making new friends. She really fought to be here. She wanted to be here.

"We were just talking on the sofa and having a little cuddle of goodbye and I just remember her suddenly crying and saying that she was going to be sad to go but she was excited to come and I remember being quite taken aback and I thought, 'Don't make me sad. I'll miss you but you'll go and have fun'."

Brother Lyle Kercher also spoke of struggling to cope with Meredith's death and said of the new guilty verdicts: "It's not the end of it. It's another chapter moving things forward."

He told the programme: "Anybody losing anyone close is hard, losing someone so young and the way we did is obviously 100 times worse, and on top of that to have all the media attention that has gone for so long makes it very difficult to cope with."

Meredith, from Coulsdon, Surrey, was discovered with her throat slashed in her bedroom at the house she shared with fellow exchange student Knox on November 2, 2007.

Prosecution lawyer Manuela Comodi was also interviewed for the documentary, and said it would have been "impossible" for just one person to have killed her.

"One person couldn't, all at the same time, hold Meredith still and hold back her hands - because there are very few defensive wounds - inflict those wounds with a smaller knife and then give her the fatal blow with the larger knife. It is impossible. Not even superman could do it," she said.

"The principal evidence was mixed blood traces from which were extracted mixed DNA of Amanda and Meredith. The only explanation for that mix is that Amanda was bleeding and touched objects that were covered in Meredith's blood. There's no other explanation."

Much has also been made of Knox's allegedly liberal attitude to sex and relationships during the much-scrutinised saga.

Another prosecution lawyer, Giuliani Mignini, said: "The erotic game was always part of the case. I think that night Amanda wanted to make Meredith pay for judging her, which she found offensive."

Last month Knox, who did not attend her second trial, was sentenced to 28 years and six months while Sollecito was jailed for 25 years.

The pair were originally found guilty of murder in 2009, and were handed jail terms totalling more than 50 years before being cleared two years later. The appeal court went on to order a fresh trial in March last year.